This invention relates to an improved method of forming high density metal articles from metal powder. More particularly, the invention relates to a method for direct pressing and forging of articles from preheated loose metal powder contained in a substantially closed deformable metal container. The improvement is particularly suited to the forging of powders of aluminum and its alloys.
Methods of hot forging of high density metal articles from metal powder are known in the field of powder metallurgy. In general practice metal power flows into a die cavity where it may be pressed or compacted into an intermediate shape before it is forged into a shape of a final article. At the pressing stage to form an intermediate shape, heat may be added to aid interparticle bonding to form a compact of metal powder. Metal powder may also be cold compacted, i.e. pressed without the addition of heat, into an intermediate shape. These compacts are sintered and repressed into another intermediate shape, or are forged into the finished shape of the worked article.
It is further known in the art of fabricating powdered metal to place metal powder in a deformable container and to compact the powder in the container to the desired density and shape by techniques such as rolling, extruding and forging of the power-filled container. The powdered metal may be compacted into compacts which are stacked in a metallic container and the container and compacts evacuated, heated and deformed as in the forging method described in U.S. Pat. No. 3,899,821, granted Aug. 19, 1975. A metallic container filled with loose powder can be sealed, evacuated, heated and deformed in compacting the metal powder into an article of high density by applying a compressive force axially in a longitudinal portion of an extrusion chamber. U.S. Pat. No. 3,631,583, granted Jan. 4, 1972, describes such a method. Hot-rolling of an evacuated, sealed, heated container filled with metal powder is shown in U.S. Pat. No. 3,866,303, granted Feb. 18, 1975. Thus the prior art practices include cold compacting and sintering, cold compacting and hot repressing, or hot forging of powder in sealed containers. Such methods add to the complexity of forging operations in that effort and apparatus are needed to evacuate the air from the powder-filled container, to seal the container, to compact the powder to an intermediate shape and to reheat the powdered material. It is desirable, therefore, to provide a less complicated method of forging metal powder that eliminates the steps of compacting to an intermediate shape and sintering while providing a forged article having improved mechanical properties and metallurgical characteristics.